Abstract
We have made detailed studies of pyrochlore compounds, R
2Mo
2O
7 with
R=
Nd,
Sm,
Gd,
and Dy. For R=Nd and Sm, we found that apart from the ferromagnetic transition of Mo moments there is another transition of a reentrant spin glass type at lower temperatures, where both the magnetization and heat capacity data show anomalous features. We also observed that the AC susceptibility data are clearly frequency-dependent even in the ferromagnetic phase. In our pressure-dependent magnetization studies, the magnetization data of (Gd
1−
x
Dy
x
)
2Mo
2O
7 for
x=0,
0.1,
0.2
, and 0.4 are found to decrease continuously with pressures and, simultaneously, the ferromagnetic transition temperatures move towards lower temperatures. Eventually the ferromagnetic state of (Gd,Dy)
2Mo
2O
7 becomes unstable at higher pressures, and gives way to a spin glass phase that is found to exist at lower temperatures.